Properties and production methods of graphene have been under extensive study for several years. Graphene has unique electrical properties, e.g. high charge carrier mobility etc., which are ultimately promising for electronic applications. Graphene has also promising mechanical properties and therefore has been suggested for several applications on the basis of its strength or lubricative properties as well. Particles of graphene are commonly called graphene platelets, and these can be used as part of other materials or electronic devices, for instance.
Several methods for producing graphene materials have been proposed in the background art. As graphene is naturally present in graphite, several of the proposed methods produce graphene by exfoliating from graphite. Other suggested production methods include deposition of graphene on surfaces.
U.S. Patent Application Publication No. US 2007/0158618 A1 discloses a nano-composite material comprising nano-scaled graphene platelets dispersed in a matrix material. Each of the platelets comprises a sheet of graphite plane or multiple sheets of graphite plane. According to the publications, the platelets are useful for fuel cell and battery applications and can also be used in automotive friction plates and aircraft brake components.
U.S. Patent Application Publication No. US 2008/0248275 A1 discloses a nano-scaled graphene article comprising a non-woven aggregate of nano-scaled graphene platelets. According to the publications, the articles can be used for thermal management in micro-electronic devices and for current-dissipating on an aircraft skin against lightning strikes.
Liang, X et al. Graphene Transistors Fabricated via Transfer-Printing in Device Active-Areas on Large Wafer, Nano Letters, Vol. 7, No. 12, 3840-3844, 2007, discloses a method that uses pillars on a stamp to cut and exfoliate graphene islands from graphite and then uses transfer printing to place the islands from the stamp into device active-areas on a substrate. The publication also reports transistors fabricated from the printed graphene.
U.S. Patent Application Publications No. US 2008/0206124 A1 and US 2008/0258359 A1 disclose providing a graphite intercalation compound comprising a layered graphite containing expandable species residing in an interlayer space of the layered graphite Then, the method comprises exposing the graphite intercalation compound to an exfoliation temperature to at least partially exfoliate the layered graphite.
U.S. Patent Application Publication No. US 2008/0279756 A1 discloses a method of exfoliating a layered material (e.g., graphite and graphite oxide) to produce nano-scaled platelets. The method comprises dispersing graphite or graphite oxide particles in a liquid medium containing therein a surfactant or dispersing agent to obtain a suspension or slurry, and exposing the suspension or slurry to ultrasonic waves (ultrasonication) to produce the separated nano-scaled platelets.
International Patent Application Publication No. WO 2007/097938 A1 discloses graphene layers epitaxially grown on single crystal substrates. A produced device comprises a single crystal region that is substantially lattice-matched to graphene. A graphene layer is deposited on the lattice-matched region by means of molecular beam epitaxy (MBE), for instance.